Blends derived from interpolymers of an .alpha.,.beta.-unsaturated dicarboxylic acid or anhydride combined with a polar resin such as a polysulfone or a polycarbonate, together with other blend components are known. For example, U.S. Pat. No. 4,289,668 to Li discloses polymer systems plasticized with a hydroxy substituted fatty acid wherein the polymer system contains such an interpolymer and can additionally be combined with a polar resin. The fatty acid is incorporated into the blend specifically to improve its processability and flowability, manifesting its addition by lowering torque relative to the unplasticized blend. The patentees state that their plasticized resin system is characterized by improved heat resistance. It has been found, however, that including a hydroxy substituted fatty acid in such a blend lowers the blend's heat distortion temperature, detracts from dimensional stability, and makes the blend relatively susceptible to severe staining by food and blistering in cooking applications.
Other patents disclose various blends which include components selected from interpolymers of unsaturated dicarboxylic acid compounds, polycarbonates, polyarylates, and poly(aryl ether) resins. U.S. Pat. No. 4,469,843 to Lordi discloses thermoplastic molding compositions which comprise a rubber modified styrene-maleic anhydride non-equimolar copolymer and polycarbonate resin. U.S. Pat. No. 4,126,602 to Salee discloses aromatic polyester compositions comprising a linear aromatic polyester and a polymer comprising the reaction product of a styrene/maleic anhydride copolymer and a diene rubber. U.S. Pat. No. 3,966,842 to Ludwig et. al., discloses thermoplastic compositions obtained by blending specified proportions of a polycarbonate resin with a rubber-reinforced styrene/maleic anhydride copolymer. U.S. Pat. No. 3,792,115 to Kishikawa et. al. discloses thermoplastic resin compositions comprising polycarbonate resin and polyarylene ester.
None of the above patents disclose that an interpolymer containing unsaturated dicarboxylic acid moieties blended with a polyarylate, a polycarbonate, a poly(aryl ether) resin, or a polyetherimide would be suitable for use as microwave cookware, nor do these patents address the special problems which must be considered in the manufacture of cookware such as heat resistance coupled with stain resistance.
Microwave cookware articles must possess dimensional stability adequate to readily withstand moderate temperature environments like those generated by heating food in a microwave field (typically on the order of at least about 250.degree. F.), coupled with stain resistance which permits using the cookware with substantially all foods. Stain resistance is a particularly important feature when using microwave cookware to cook foods containing staining pigments such as carotenoids contained in ketchup, mustard, and many vegetables. Importantly, materials for microwave cookware should also possess toughness so that articles made therefrom are not easily broken by dropping, and should be readily thermoformable as by injection molding so that more expensive manufacturing procedures (e.g., such as compression molding) need not be employed.
U.S. Pat. No. 4,503,168 to Hartsing, Jr. discloses cookware formed from a polyarylethersulfone which may be blended with a poly(aryl ether) or a thermoplastic polymer selected from polyarylates, polyetherimides, polyesters, aromatic polycarbonates, styrene resins, poly(alkyl acrylates), polyhydroxyethers, poly(arylene sulfides), and polyamides. The patent does not disclose the cookware of this invention.